What this means
The IEEE assigned the MA-M block 78E9962 to STIEBEL ELTRON GMBH & CO. KG. Every network interface they manufacture under this block has a MAC address beginning with these digits, followed by a unique per-device identifier. If a device on your network shows a MAC starting 78:E9:96:2, it is STIEBEL ELTRON GMBH & CO. KG hardware.